Urinary stones often contain a mixture of insoluable crystalline components. Based on the highly specific orientation of the crystals usually found in these stones the proposal has been advanced that epitaxial crystal growth relationships are involved in the growth of the urolithiasis. Although the arguments are based on acceptable theoretical considerations there is, as yet, little direct experimental evidence proving or denying the existence of epitaxy among the various crystalline components found in human urinary stones. The objective of this investigation is to experimentally establish the epitaxial relationships that are operative under simulated in vivo conditions. The procedure will be to measure the kinetics of epitaxially induced crystal growth of the major components of urinary stones. The relative ability of each urinary stone component to induce precipitation from a stable supersaturated solution of other stone materials will then be used to predict whether a particular crystal growth system is a likedy contributor to mixed urolithiasis. The chemical kinetic studies will be supplemented by scanning electron microscope observation of the crystalline material obtained from the crystal growth experiments. In the systems in which epitaxy appears to be important in urolithiasis a further study will be made to determine the conditions under which the induced precipitation upon a foreign crystalline material is prevented or delayed. This study will involve the use of known crystal growth inhibitors.